How do I earn money for a laptop?

I am 12 yrs old and i need to earn money but mom is strict so i cant work for neighbors even though we have lived my house for 3 years and know the neighbors very well.I want to buy a mini laptop and its 348.00 and i want it bad!!! I am verrrry responsible and i have a fifteen yr old sister and my mom sys im am more responsible than her. PLEASE HELP